Ultrasonic array transducer

ABSTRACT

The present invention provides an ultrasonic probe and method for making the same is provided which has an advantageous construction and method of assembly. The ultrasonic probe has a segmented ultrasonic transducer having a plurality of individual independent transducers, a plurality of piezoelectric transducers connected to a first end of a respective individual independent transducer; and a plurality of electrical connections electrically communicating each the piezoelectric transducer with a power source.

PRIORITY CLAIM

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/471,646 filed on Dec. 23, 1999, now abandoned and entitledUltrasonic Array Transducer.

FIELD OF THE INVENTION

The present invention relates to an ultrasonic array transducer, andmore particularly, to an ultrasonic array transducer fornon-destructively inspecting a weld joint.

BACKGROUND OF THE INVENTION

Welding is a common process for attaching one metal member to another.This process generally involves heating an interface between the itemswhich are to be welded, thereby melting the interface into one joint orweld nugget. Because this process has its application in many differenttypes of manufacturing, such as automobile manufacturing, inspectionensuring that the weld nugget meets certain quality standards is a must.Specifically, it is desirable to inspect the area, size andconfiguration of the weld nugget and to determine if any defects existtherein. Uninspected welds may result in weld failure after the weldeditem is sold or distributed to a final user.

Ideally, a weld is inspected either during or shortly after the weldingprocess so that added inspection does not increase weld time, and toallow weld problems to be identified when they occur. Furthermore,non-destructive testing is preferred so that welded parts which passinspection may still be sold or distributed to the end user after theyhave been tested.

Visual inspection systems have been employed in the weld environment forthis purpose. Specifically, an individual, such as a quality controlperson, may gage the size of the weld nugget or destructively test awelded item to determine its internal characteristics.

While weld systems do provide a quantitative analysis of the size of theweld nugget, visual inspection has some drawbacks. First, because of thebright light and harsh conditions generated by welding, visualinspection of a weld cannot be performed during the welding process.Instead, the welded item must be inspected off line, adding more timeand cost to manufacturing. Second, to properly inspect the weld fordefects, the internal structure of the weld nugget must be observed.This, in many instances, requires the welded item to be destructivelytested, rendering the welded item useless. Besides the increased costassociated with scrapping an item for the purpose of inspection, it ispractically impossible to destructively test all items. As such,destructive testing results in a lower number of samples tested andincreased cost to manufacturing.

Devices and methods developed to inspect welds and other obscured itemsare generally disclosed in U.S. Patent Applications entitled TRANSDUCERBUILT INTO AN ELECTRODE and MULTIEYED ACOUSTICAL MICROSCOPIC LENSSYSTEM, invented by Maev et al. and assigned to the assignee of thepresent application and hereby incorporated by reference. While thesedevices and methods do provide a means for analyzing welded joints, theydo not provide the quantitative accuracy sometimes required bymanufacturers.

In view of the above, it would be desirable to manufacture an ultrasonicarray transducer which is able to non-destructively test a weld subjectand which has a high degree of resolution.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide anultrasonic array transducer able to non-destructively inspect a weldjoint.

It is yet another object of the present invention to provide anultrasonic array transducer which has a high density of acoustical soundgenerating units for increasing resolution.

In accordance with the broad teachings of this invention, an ultrasonicprobe and method for making the same is provided which has anadvantageous construction and method of assembly. The ultrasonic probehas a segmented ultrasonic transducer having a plurality of individualindependent transducers, a plurality of piezoelectric transducersconnected to a first end of a respective individual independenttransducers, and a plurality of electrical connections electricallycommunicating each the piezoelectric transducer with a power source.

In another aspect of the present invention, the power source comprises apulser-receiver in electrical communication with a multiplexer. Themultiplexer, in turn, is in electrical communication with the pluralityof piezoelectric transducers. The pulser-receiver is responsive to themultiplexer to provide a display representative of acoustical imagesreceived by the piezoelectric transducers.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating preferred embodiments of the invention, are intended forpurposes of illustration only, since various changes and modificationswithin the spirit and scope of the invention will become apparent tothose skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings which illustrate the best mode presently contemplatedfor carrying out the present invention:

FIG. 1 is an exploded view of an ultrasonic array transducer accordingto the present invention;

FIG. 2 is a schematic view of an ultrasonic probe and data acquisitionsystem for an ultrasonic array transducer according to the presentinvention;

FIG. 3 is a perspective view of an ultrasonic probe prior to dicing foran ultrasonic array transducer according to the present invention;

FIG. 4 is a perspective view of a diced ultrasonic probe for anultrasonic array transducer according to the present invention;

FIG. 5 is a perspective view of a diced ultrasonic probe being filledwith nonconductive compound for electrical and acoustic insulationaccording to the present invention;

FIG. 6 is a perspective view of an individual independent transducer foran ultrasonic array transducer according to the present invention;

FIG. 7 is a perspective view of an ultrasonic probe connected to agrounding connector according to the present invention;

FIG. 8 is a perspective view of an ultrasonic probe being coated with aconductive material according to the present invention; and

FIG. 9 is a schematic view of an ultrasonic probe and data acquisitionsystem for an ultrasonic array transducer according to an alternativeembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiments is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

Referring now to FIG. 1, an exploded view of an ultrasonic arraytransducer 10 is shown. Ultrasonic array transducer 10 generallycomprises a segmented ultrasonic transducer 12, Z-axis conductive pad14, circuit interface board 16, and coaxial cable 18.

Segmented ultrasonic transducer 12 generally has a cluster (or clusters)of small individual independent transducers 24, which are separated by aplurality of gaps 22. Each gap 22 (also called a “kerf”) is filled witha non-conductive bonding agent which maintains the elements bondedtogether and electrically insulates them from each other.

FIG. 6 illustrates one individual independent transducer 24. Individualindependent transducer 24 is composed of an ultrasonic element, such aspiezoelectric crystal 25 (or may be any other ultrasonic element), and amatching damping body 23. Each piezoelectric transducer, when actuated,generates an ultrasonic pulse. The generation of this ultrasonic pulseis due to a physical reaction to electrical stimuli as is known in theart.

The remainder of individual independent transducer 24 is damping body23. Damping body 23 is designed to make an ultrasonic pulse generated byindividual independent transducer 24 broadband. The broadband waveensures that a definable wave front, having a sharp acoustic signature,exits each individual independent transducer 24. Damping body 23accomplishes this by the mere fact of its weight. The weight of dampingbody 23 changes the vibration characteristics of piezoelectric crystals(which will be described) which are attached to it. Specifically,piezoelectric crystals which are attached to damping body 23 vibrate inresponse to acoustical energy in such a way as to provide a greaterdefinable wave front.

Damping body 23 is preferably constructed from a mixture of glue and ahigh percentage of heavy conductive powder. The glue acts to retain theconductive powder in a solid and rigid structure. The glue is mixed withthe conductive powder in such a way as to ensure that some glue is incontact with the piezoelectric crystal 25. This glue forms the bondbetween damping body 23 and piezoelectric crystal 25. A layer ofconductive material, preferably a thin conductive coating, is coated onthe exposed surface of piezoelectric crystal 25. This layer extendsalong the entire surface of ultrasonic probe 10 and provides a groundingcircuit therefor (as will be discussed in greater detail).

Z-axis conductive pad 14, as is known in the art, provides a pluralityof conductive paths from one element such as a circuit board to a secondelement. In the present invention, Z-axis conductive pad 14 provides aplurality of conductive paths from piezoelectric crystal 25 to circuitinterface board 16.

Circuit interface board 16 is divided into a plurality of areas 34. Eacharea 34 combines with a respective area on z-axis conductive pad 14 toform a plurality of conductive paths having the closest possibleresemblance with the cross section of the segmented ultrasonic matrix10. Thereby, each path communicates with a respective individualindependent transducer 24.

Each coaxial cable 18 is connected to a different area 34 of lower face36 of circuit interface board 16, preferably by soldering. Thisconnection, in conjunction with the other electrical connectionsdiscussed above, allows each coaxial cable 18 to provide electricalpower to a respective side of piezoelectric crystal 25 which is oppositedamping body 23. As such, power supplied by coaxial cable 18 actuatespiezoelectric crystal 25 electrically communicates with damping body 23to ground through the layer of conductive material on piezoelectriccrystals 25. It is noted that coaxial cable 18 can connect to circuitinterface board 16 by a conductive layer that is a soft printed circuitboard ribbon conductor.

Referring now to FIG. 2, a fully assembled ultrasonic array transducer10 is shown including multiplexer 42, pulser-receiver 44, and computer46. Segmented ultrasonic transducer 12 is connected to multiplexer 42through cable assembly 18. Multiplexer 42, in turn, communicates withpulser-receiver 44 by connections 54 and 56. Pulser-receiver 44communicates with computer 46 through serial interface 52. Finally,computer 46 is electrically attached to multiplexer 42 by parallel portconnection 48. It is noted, however, that computer 46 can alsocommunicate with multiplexer 42 through serial interface 52 and withpulser-receiver 44 through parallel port connections 48 or through anyother possible interface.

With continued reference to FIGS. 1 and 2, the operation of the presentinvention will now be described. Welded item 62 is first positionedunder ultrasonic probe 10. Ultrasonic probe 10 can be connected to thesurface of the welded item in a number of ways, such as via solid orliquid delays or soft elastomeric delays or in direct contact withoutdelays. Preferably however, before ultrasonic probe 10 is placed inphysical contact with welded item 62, an ultrasonic gel is layeredbetween the two elements to increase the efficiency which soundgenerated from piezoelectric crystal 25 is transferred to welded item62. Computer 46 next instructs pulser-receiver 44 to send an electricalpulse to multiplexer 42. Computer 46 instructs multiplexer 42 to sendthis pulse to a specific wire 18 corresponding to a specific individualindependent transducer 24. The signal travels from one of the wires ofcable assembly 18, through an area 34 of circuit interface board 16 andthrough Z-axis conductive pad 14 to a respective individual independenttransducer 24. This electrical signal is ultimately grounded bytraveling across the conductive coating on piezoelectric crystals 25 andout to grounding connection 27. Piezoelectric crystal 25 generates anacoustical pulse, in response to the electrical signal, which propagatestoward welded item 62. Acoustic energy reflected from welded item 62oscillates piezoelectric crystal 25, thereby inducing a current backinto wire 18. This process is repeated for each piezoelectric crystal 25until all individual independent transducers 24 have been fired. Thereceived signals from individual independent transducers 24 areinterpreted by pulser-receiver 44 to develop a plurality of A-scans, oneA-scan per individual independent transducer 24. Computer 46 thencompiles all of the generated A-scans from pulser-receiver 44 anddevelops a C-scan therefrom. A method for sequentially firing allpiezoelectric transducers 28 and analyzing signals received therefrom toform A-scans and subsequent C-scans is generally disclosed in U.S.patent application Ser. No. 09/303,301 filed Apr. 30, 1999, and entitledMULTIEYED ACOUSTICAL MICROSCOPIC LENS SYSTEM, invented by Maev, et al.assigned to the assignee of the present application, and herebyincorporated by reference.

It is noted, however, various possible modes of operation are availablefor the present invention. Such modes include through-transmission,pitch-catch, tandem and other modes. In such modes, two ultrasonictransducers are used. Preferably, one transducer is a standardmonolithic transducer and the other is an ultrasonic array transducer 10as described above. Generally, the monolithic transducer is used fortransmission by creating a distribution of acoustic energy that passesthrough the welded item, as modified by the welded item's geometry,material properties, and flows, and is received by the ultrasonic arraytransducer 10. The ultrasonic array transducer 10 then reads theacoustic energy and provides a means for visual presentation of thecharacteristics of the welded item, whereby nondestructivecharacterization of the welded item is possible. In addition, thestandard monolithic transducer can be positioned directly on top of theindividual independent transducers 24, opposite the Z-axis conductivepad 14.

Another mode of operation is enabled by a variation of the ultrasonicarray transducer 10′ including a segmented ultrasonic transducer 12having a cluster of independent transducers 24 separated by gaps 22filled with a non-conductive bonding agent, combined with monolithicpiezoelectric element 100 installed adjacent the ultrasonic array withina housing 110, as shown in FIG. 9. Each transducer 24 preferablyincludes a piezoelectric crystal 25 (or other ultrasonic element) and adamping body 23. The monolithic piezoelectric element 100 is connectedto the pulser-receiver 44, which communicates a burst of ultrasonicenergy through the ultrasonic array transducer 10′ and to the weldeditem. The transducers 24 act as a multi-element receiver producing a mapof the field useable for various purposes such as imaging, monitoring,and measurement. Preferably, a plurality of coaxial cables 18 areconnected to a Z-axis conductive pad 14 for transmitting the acousticsignal to the multiplexer 42. Alternatively, a soft-printed circuitboard ribbon conductor can be used in place of the plurality of coaxialcables 18.

Other modes of operation are disclosed in U.S. patent applications Ser.No. 09/283,397, filed Apr. 1, 1999, entitled TRANSDUCER BUILT INTO ANELECTRODE and Ser. No. 09/303,301, filed Apr. 30, 1999, and entitledMULTIEYED ACOUSTICAL MICROSCOPIC LENS SYSTEM, both invented by Maev etal., assigned to the assignee of the present application, and herebyincorporated by reference.

Referring to FIGS. 3-5, 7 and 8, the assembly of the present inventionwill now be described. In FIG. 3, a cylindrical uniformly shaped pieceof damping material 64 is shown with a wire saw 66 and piezoelectriccrystal 28 positioned over it. Such uniform shapes include cylinders,rectangles, ellipses, triangles and all other shapes which can be slicedup and down to form a plurality of smaller width, yet similarly shaped,elements. Piezoelectric crystal 28 is disc like in shape and matches thegeometrical configuration of damping material 64. In the firstoperation, piezoelectric crystal 28 is attached to damping material 64through a molding process and preferably uses the glue in the buffermaterial 64 for attachment. Next, ultrasonic buffer material 64 is sawedin a criss-cross fashion by wire saw 66. As shown in FIG. 4, this sawingextends downward a length 68 within the material and forms gaps 22. Theconfiguration of the gaps 22 define the outer bounds of each individualindependent transducer 24. As shown in FIG. 5, harness 68 is thenpositioned around the cut portion of ultrasonic buffer material 64.Harness 68 acts to encapsulate the newly formed individual independenttransducers. Then, an epoxy or other bonding agent which is electricallyand mechanically insulating is poured into gaps 22 by nozzle 70. Thisepoxy ensures that each individual independent transducer iselectrically insulated from the remaining individual independenttransducers and acts to keep the individual independent transducers 24together in a fixed configuration. After the epoxy cures, the sawedportion of ultrasonic damping material 64 is separated from the unsawedportion. Grounding connections 27 are attached to the exposed ends of afew piezoelectric crystals 25. Referring now to FIG. 8, a coating ofconductive material, preferably Al or Au is sprayed over the surface ofthe exposed sides of piezoelectric crystals 25. This coating acts toprovide a conductive layer which connects each respective end ofpiezoelectric crystal 25 along side 29 with grounding connection 27.

Coaxial cables 18, containing a plurality of wires, is then attached tocircuit interface board 16. Each wire of coaxial cable 18 is bonded toeach area 34 of circuit interface board 16. Z-axis conductive pad 14 isthen positioned between circuit interface board 16 and segmentedultrasonic transducer 12. Z-axis conductive pad 14, circuit interfaceboard 16 and individual independent transducer 24 is then sandwichedtogether, thereby providing electrical passage from each respective wireof coaxial cable 18 and area 34 to a resulting individual independenttransducer 24. It is noted that preferably only a frictional engagementexists between z-axis conductive pad 14 and the other sandwichedelements. This sandwiching eliminates the requirement that each elementmust be mechanically attached by solder or other affixing method. Ashell or other form of housing can then be placed around the resultantultrasonic probe 10.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention. Such variations ormodifications, as would be obvious to one skilled in the art, areintended to be included within the scope of the following claims.

What is claimed is:
 1. An ultrasonic array transducer comprising: asegmented ultrasonic transducer having a plurality of individualindependent transducers bonded together by a nonconductive bondingagent, each said individual independent transducer including apiezoelectric crystal bonded to a damping body; a connector having afirst end and a second end, said connector electrically connecting eachsaid individual independent transducer with a power source, saidconnector providing an independent electrical path such that each saidindividual independent transducer is powered independently from aremainder of said individual independent transducers, and a groundingconnection grounding said individual independent transducers, wherebysaid connector and said grounding connection forms a complete circuit toenergize said individual independent transducers.
 2. The ultrasonicarray transducer as claimed in claim 1, wherein said power sourcecomprises a multiplexer in electrical communication with apulser-receiver and a computer and said connector, said pulser-receiverresponsive to said individual independent transducers to provide adisplay representative of acoustical images received by said individualindependent transducers.
 3. The ultrasonic array transducer as claimedin claim 2, wherein said multiplexer is responsive to said computer tochannel electrical signals from said pulser-receiver to a selected oneof said plurality of individual independent transducers.
 4. Theultrasonic array transducer as claimed in claim 3, wherein said computeris responsive to said pulser-receiver to develop an A-scan from saiddisplay representative of acoustical images.
 5. The ultrasonic arraytransducer as claimed in claim 4, wherein said computer is responsive tosaid A-scan to develop a C-scan.
 6. The ultrasonic array transducer asclaimed in claim 1, further comprising a Z-axis conductive padpositioned between the first end of said connector and said plurality ofindividual independent transducers, said z-axis conductive padelectrically connecting said connector to said plurality of individualindependent transducers.
 7. The ultrasonic array transducer as claimedin claim 1, further comprising a monolithic piezoelectric elementinstalled adjacent the segmented ultrasonic transducer within a housing.8. The ultrasonic array transducer as claimed in claim 7, wherein thepower source comprises a multiplexer and electrical communication with apulse receiver, a computer, and said connector, said pulse receiver inelectrical communication with said monolithic piezoelectric element tocommunicate ultrasonic energy through said segmented ultrasonictransducer to provide a display representative of acoustical imagesreceived by said individual independent transducers.
 9. The ultrasonicarray transducer as claimed in claim 8, further comprising a Z-axisconductive pad for transmitting an acoustic signal from said segmentedultrasonic transducer to said multiplexer.
 10. The ultrasonic arraytransducer according to claim 9, further comprising a plurality ofcoaxial cables in electrical communication with said Z-axis conductivepad and said multiplexer for transmitting said acoustic signal.
 11. Theultrasonic array transducer according to claim 10, wherein said computeris responsive to said pulse receiver to develop an A-scan from saidultrasonic energy communicated through said segmented ultrasonictransducer.
 12. The ultrasonic array transducer according to claim 11,wherein said computer is responsive to said A-scan to develop a C-scan.